B4.4 - Uncertainties of a Linear Variable Differential Inductor Probe for Picometer Resolution Measurement Systems

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B4 - Mechanical Sensors II
B. Aschenbrenner, B. Zagar - Johannes Kepler University Linz (Austria)
288 - 293


The ever increasing quality demand of machine components and machines in industry has been the driving force behind research for more accurate measurement methods. Precisison measurement systems that can achieve a displacement accuracy in the order of sub-nanometers are essential in the optical, semiconductor and nanotechnology industry and ultraprecise machining. In the proposed paper we discuss a range of parameters that can potentially lead to un- certainties in a highest resolution displacement system. A Linear Variable Differential Inductor (LVDI) is used as position sensor. This kind of sensor can measure displacements down to the subnanometer range. Even under rough conditions the LVDI guarantees a good repeatability of the measurement.
In systems that strive for sub nm-resolution even usually safely ignored influencies like static friction, dynamic friction, heating, elastic deformation, stochastic noise and many more can result in uncertainties of several nanometers. Pretty much every conceivable, enviromental parameter needs to be analyzed for its possible influence.
The purpose of this research is to clarify the influences of some of the parameters in ultraprecision measurement. The analyzed uncertaities will also occur in other sensor principles and are thus important, too. In this contribution some easily overlooked sources of errors in the pm-range, will be discussed and it is shown that each error term can be orders of magnitude larger than typical resolution that a user assumes for these systems.
Several important numbers of influencies are considered and calculated and a mathematical model is developed to calculate the measurement uncertainties of elastic deformation due to measuring force between the probe and the device under test. Elastic deformation occurs where a mechanical force is excerted on a specimen through a tactile sensor. Even at contact forces as low as 0.1 N elastic deformaton may account for nanometers and contribute to the measurement uncertainty.
Analyzing the above mentioned error sources one can quickly see that all of them, if not taken care of appropriately, carry the potential to cause significantly larger deviations than the resolution sought after demands.